Should I carry on regardless and continue in my attempt to build a life, or should I end it and remain single?
Aaaw OP - nobody can advise you what to do here. It;s your life, & the implications of any choices far too large to be made for you.
But I'd like to offer a word of caution - beware that the One That Got Away is too easy to idealise. You've never had to experience the reality of a romantic relationship or expactations with them, it's not based on any dady-to-day grind that actual relationships are subject to.
Has anyone else experienced this?
Yeah - me & my oldest mate.
Each or one of us coupled up bar a few separate periods over 5 decades of excellent friendship.
He made the first move - I rejected it due to then being in a (lousy!) relationship with our mutual friend.
I very carefully didn't make the second move, when we were each divorcing, coincidentally simultaneously. It was not the Right Thing To Do. We were each far too good to be used as each other's rebound - let alone emotional scapegoats (both escaped abusive spouses - crazy-making). We needed to deal with the healing & fallout first.
Instead, I gave myself a good talking to & studied up on limerence & why people knee-jerk they way into fast turnover romances when they ought to be staying single & Doing The Work. My mate met his now wife toward the end of that period, so once I was over the worst of it, I told him, as I needed to stay away from him while he was in the first painful (to me!) flush of infatuation.
We've both thought even better of each other for staying friends, & have never had to risk losing each other to the vagaries "falling in love" & then "out". We see each other as family members now the more youthful, ahem, urges have settled, so it would just feel incestuous to dabble there, even were he to become single again. I'm happy to have a lifelong pal who I can lean on like a loyal sibling, & vice versa.
But you may feel very differently. I'm just advising you to not pine after your pal with rose-tinted specs. And if you want to risk romance with him - be utterly clear & straightforward about it, letting him know that you don't in any way wish to devalue your long term friendship by 'asking him out'.
I feel for you OP. But love is a willed state of mind, an action, a daily decision to keep loving. Love also takes many forms. Only you can decide which form is most valuable to you, & what is worth risking. 